A key component of most computers is an assembly that is referred to as a magnetic disk drive, or hard disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
Perpendicular magnetic recording, wherein the recorded bits are stored in a perpendicular or out-of plane orientation in the recording layer, is a promising path toward ultra-high recording densities in magnetic recording hard disk drives. One type of perpendicular magnetic recording system is a system that uses a dual layer media. The dual layer media includes a perpendicular magnetic data recording layer formed on a soft or relatively low coercivity magnetically permeable under-layer. The under-layer serves as a flux return path for the field from the write pole to the return pole of the recording head. The magnetic transitions between adjacent oppositely direct magnetized regions are detectable by the read element or head as the recorded bits.
Other variations of granular media have been explored for use in magnetic data recording systems as well. For example, granular media that can be used with thermally assisted writing, and microwave assisted writing. Media for thermally assisted recording (TAR) may include granular materials like CoPtCr, FePt, CoPt and other alloys. Media for microwave assisted writing may include granular materials like CoPtCr, FePt, CoPt and other alloys.
One type of material that can be used as a recording layer is a granular ferromagnetic cobalt (Co) alloy, such as a CoPtCr alloy, with a hexagonal-close-packed (HCP) crystalline structure having the c-axis oriented substantially out of plane or perpendicular to the plane of the recording layer. The granular cobalt alloy recording layer should also have a well-isolated fine-grain structure to produce a high coercivity (Hc) media and to reduce inter-granular exchange coupling, which is responsible for high intrinsic media noise. Enhancement of the grain segregation in the cobalt alloy recording layer can be achieved by the addition of oxides, including oxides of Si, Ta, Ti and Nb. These oxides tend to precipitate to the grain boundaries, and together with the elements of the cobalt alloy, form a non-magnetic inter-granular material.
The Co alloy recording layer has substantially out of plane or perpendicular magnetic anisotropy as a result of the c-axis of its HCP crystalline structure being induced to grow substantially perpendicular to the plane of the layer during deposition. To induce this growth of the HCP recording layer, the inter-layer onto which the recording layer is formed is also an HCP material. Ruthenium (Ru) and certain Ru alloys, such as RuCr, are non-magnetic HCP materials that can be used for the inter-layer.
The enhancement of segregation of the magnetic grains in the recording layer by the additive oxides is important for achieving high areal density and recording performance. The inter-granular oxide material not only decouples inter-granular exchange, but also exerts control on the size and distribution of the magnetic grains in the recording layer. Current disk fabrication methods achieve this segregated recording layer by growing the recording layer on a Ru or Ru-alloy interlayer that exhibits columnar growth of the Ru or Ru alloy grains. The columnar growth of the interlayer is accomplished by sputter depositing it at a relatively high sputtering pressure.
However, such a process results in a recording layer having a relatively wide variation in the size of the magnetic grains. A large grain size distribution is undesirable because it results in a variation in magnetic recording properties across the disk and because some of the smaller grains can become thermally unstable, resulting in a loss of data. There is, therefore, a need for a magnetic media having uniform grain structure, and also for a recording system that can effectively record to such a recording medium without excessive signal noise or bit error rate.